In today's as well as future electrical systems of motor vehicles, in particular hybrid or electric vehicles, high-performance DC voltage converters (frequently also referred to as DC/DC converters) are necessary to be able to regulate the energy flow between various voltage levels. Thus, in start-stop systems, for example, a voltage drop in the vehicle electrical system during starting is compensated for by a DC voltage converter. The existing cost, installation space, and weight constraints in the automotive field are taken into account by using so-called multiphase DC voltage converters. The power to be transmitted is distributed over multiple converter units or phase modules connected in parallel. The individual phase modules are preferably controlled in a phase- or time-shifted manner. As a result of the phase-shifted control, the current ripples in the superimposed output signal are significantly decreased, and the frequency of the output signal of the DC voltage converter is increased by the number of converter units which are clocked in an offset manner relative to the base clock frequency of the converter units. Costs for and volumes of output filters of the DC voltage converter may be reduced in this way.
To be able to make effective use of the above-mentioned advantage for multiphase DC voltage converters, the currents must generally be uniformly or “symmetrically” distributed over the individual converter units or phase modules.
The use of multiphase DC voltage converters having coupled coils in the automotive field is described in J. Czogalla, J. Li, C. Sullivan: Automotive Application of Multi-Phase Coupled-Inductor DC-DC Converter, 0-7803-7883-0/03, IEEE, 2003.